Spinning is a manufacturing process where a part is formed by being subjected to the forming stresses applied by a roller (or rollers) many times. Each element of metal is brought into the material's plastic region for a very short period of time and formed. The process repeats as many times as required. The ability to form the part an almost limitless number of times gives spinning a great advantage over other processes such as press forming. Some parts can only be practically made by a spinning process in order to be technically and commercially acceptable.
A state of the art for spinning pulleys is known as the split metal process, where the edge of a round metal blank is formed into the pulley sheaves. Spinning pulleys requires high clamping forces on a blank between a headstock and a tailstock tooling. The clamping force for automotive type pulleys is between 40 to 60 metric tons. The clamped part rotates at 400 to 1000 rpm. As it rotates it is exposed to side loads from forming rolls with pressures in the range of about 10 to 15 metric tons each. For typical automotive pulleys there is usually a need to use four rolls. This results in a very heavy and costly equipment as high clamping force and side loads are imposed upon rotating bearings. Hence, the state of the technology today is to make only one part at a time.
Representative of the art is U.S. Pat. No. 4,669,291 which discloses an improved multiple roller spinning machine for spinning vehicle one-piece wheels is disclosed in which the roller holder is capable of sliding in a direction parallel with the axis of spinning and has a hydraulic cylinder which moves through its axially movable piston rod the holder horizontally thereby bringing the multiple rollers sequentially in to an operating position just above the wheel material clamped between the dies of the driving and driven spindles. Each of the multiple rollers is coupled to a control hydraulic cylinder which drives through its piston the respective roller vertically between a retracted position and a drawing position where the roller is pressed against the periphery of the wheel material. Thus, not only can the sequence of different drawing steps, in a most preferable embodiment, from rough to finishing drawing, be completed in an automatic continued manner, but also operation of the hydraulic cylinder to shift the holder, with the particular roller pressed against the material periphery being set in spinning, causes the roller to draw a wider range than its size across the U-cross section portion of the periphery. According to another embodiment, the holder carries therein multiple rows of different forming rollers arranged radially about a common center such that the wheel material can be subject to drawing by multiple rollers simultaneously applied at different points about the material periphery.
What is needed is a method of simultaneously spinning two parts using an intermediate mandrel in a spinning machine. The present invention meets this need.